Melting relations in the MgO-MgSiO3 system up to 70 GPa.
Melting relations in the MgO-MgSiO3 system up to 70 GPa.
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MgO-MgSiO3 系统中的熔化关系高达 70 GPa。
DOI：
10.1007/s00269-017-0871-8
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
T.
中科院分区：
文献类型：
--
作者：
Ohnishi;S.;Kuwayama;Y.;Inoue;T.
采用CO2激光加热金刚石对顶砧装置，在70 GPa压力下对MgO-MgSiO 3二元系进行了熔化实验。用双束聚焦离子束（FIB）和场发射扫描电子显微镜（FE-SEM）分别对淬火样品进行了抛光和分析。液相线相和共晶组成的基础上确定的文本和化学分析样品的横截面。我们的实验结果表明，在35 GPa的共晶组成是Si/Mg摩尔比约0.76，它随着压力的增加而减少。在45 GPa以上，它变得相对恒定，约为0.64-0.65 Si/Mg摩尔比。利用我们的实验数据收集在一个宽的压力范围高达70 GPa连同以前的实验数据，我们已经构建了一个热力学模型的MgO-MgSiO 3系统的共晶组成。外推到地幔底部的压力和温度条件下的共晶组成约为0.64 Si/Mg摩尔比。模型化的共晶组成与来自从头计算的先前预测（de Koker等人，在Earth Planet Sci Lett 361：58-63，2013中）非常一致，表明非理想规则溶液模型的简单假设可以很好地描述MgO-MgSiO 3系统在高压下的熔化关系。我们的研究结果表明，在35 GPa下，对于简化的软锰矿成分（~0.7 Si/Mg摩尔比），液相线相从MgO-方镁石转变为MgSiO 3-Bridgmanite，而对于镁橄榄石成分（~0.84 Si/Mg摩尔比），MgSiO 3-Bridgmanite是整个下地幔条件下的液相线相。
Melting experiments in a binary system MgO–MgSiO3were performed up to 70 GPa using a CO2laser heated diamond anvil cell. The quenched samples were polished and analyzed by a dualbeam focused ion beam (FIB) and a field emission scanning electron microscope (FE-SEM), respectively. The liquidus phase and the eutectic composition were determined on the basis of textual and chemical analyses of sample cross sections. Our experimental results show that the eutectic composition is the Si/Mg molar ratio of ~0.76 at 35 GPa and it decreases with increasing pressure. Above 45 GPa, it becomes relatively constant at about 0.64–0.65 Si/Mg molar ratio. Using our experimental data collected at a wide pressure range up to 70 GPa together with previous experimental data, we have constructed a thermodynamic model of the eutectic composition of the MgO–MgSiO3system. The eutectic composition extrapolated to the pressure and temperature conditions at the base of the mantle is about 0.64 Si/Mg molar ratio. The modeled eutectic composition is quite consistent with a previous prediction from ab initio calculations (de Koker et al. in Earth Planet Sci Lett 361:58–63, 2013), suggesting that the simple assumption of a non-ideal regular solution model can well describe the melting relation of the MgO–MgSiO3system at high pressure. Our results show that the liquidus phase changes from MgO-periclase to MgSiO3-bridgmanite at 35 GPa for the simplified pyrolite composition (~0.7 Si/Mg molar ratio), while MgSiO3-bridgmanite is the liquidus phase at the entire lower mantle conditions for the chondritic composition (~0.84 Si/Mg molar ratio).